1. Technical Field
The present disclosure relates to a semiconductor device and a method of forming the same, and more particularly, to a contactless nonvolatile memory device and a method of forming the same.
2. Discussion of the Related Art
A NOR type contactless nonvolatile memory device having a virtual ground array structure includes a buried impurity diffusion region, which is formed in a semiconductor substrate and crosses word lines at right angles. The buried impurity diffusion region can be a source or a drain depending on which cell is programmed or read. A cell size can be reduced when the contact plug is not formed in every unit cell. For example, a contact plug can be formed only in the buried impurity diffusion region in both ends of a cell array.
In a cell of the virtual ground array structure, the buried impurity diffusion region is isolated from another buried impurity diffusion region by having an impurity region of an opposite conductivity therebetween. Therefore, a distance between two diffusion regions should be long enough to prevent a punch through, which can be generated between the two impurity diffusion regions.
Also, a misalignment may be caused by a decreased process margin in patterning a floating gate layer.